WASHINGTON (CNN) -- U.S. inspectors have ended their search for weapons of mass destruction in Iraq in recent weeks, a U.S. intelligence official told CNN.

The United States is taking steps to determine how it received erroneous intelligence that deposed Iraqi leader Saddam Hussein was developing and stockpiling nuclear, chemical and biological weapons, White House spokesman Scott McClellan said Wednesday.

"Our friends and allies had the same intelligence that we had when it came to Saddam Hussein," he said. "Now we need to continue to move forward to find out what went wrong and to correct those flaws.

"That's exactly what the independent commission the president appointed is going to do," McClellan said. "They're going to make recommendations, and the president is committed to acting on those recommendations."

At the same time, he said, President Bush stands by the decision to invade Iraq.

"We had a regime that had a history of using weapons of mass destruction and had a history of defying the international community and had a history of ties to terrorist organizations in Iraq," he said. "We had the attacks on September 11 [2001], that taught us we must confront threats before it's too late.

"That's what the president's committed to doing," he said. "Because this is about making America more secure."

The search ended almost two years after President Bush ordered the invasion of Iraq, saying intelligence indicated Saddam was building weapons of mass destruction and may have hidden weapons stockpiles.

Members of the Iraq Survey Group were continuing to examine hundreds of documents and would investigate any new leads, the U.S. intelligence official said.

Charles A. Duelfer, who headed the Iraq Survey Group's search for WMD in Iraq, has returned to the United States and is working on his final report, the official said.

Many of the military and intelligence personnel who had been assigned to the weapons search are now working on counterinsurgency matters, the official said.

Asked whether the Bush administration planned to announce the end of the physical WMD search, McClellan deferred to Duelfer.

"I think it's up to him to make those determinations," McClellan said.

State Department spokesman Richard Boucher said though the search for WMD yielded no results, the United States, based on "extensive intelligence," believed before it invaded Iraq that Saddam was intent on acquiring them.

A State Department program has employed about 120 Iraqi scientists with expertise in WMD to undertake research in other fields of science, he said.

A spokesman for the British Foreign Office said that though the physical search is over, some work continues.

"The hunt for WMD will continue under whatever authority is in charge, right now the Iraqi interim government," he said.

Invasion defended

In October, Duelfer released a preliminary report finding that in March 2003 -- the month of the invasion -- Saddam did not have any WMD stockpiles and had not started any program to produce them.

The Iraq Survey Group report said that Iraq's WMD program was essentially destroyed in 1991 and Saddam ended the country's nuclear program after the Persian Gulf War in 1991.

The report found that Iraq worked hard to cheat on United Nations-imposed sanctions and retain the capability to resume production of weapons of mass destruction at some time in the future. (Full story)

"[Saddam] wanted to end sanctions while preserving the capability to reconstitute his weapons of mass destruction when sanctions were lifted," a summary of the report said.

After Duelfer delivered his Iraq Survey Group's report to the Senate, Bush acknowledged that Iraq didn't have weapons of mass destruction at the time he ordered the invasion but said Saddam was "systematically gaming the system" and that the world is safer because he is no longer in power.

The preliminary report indicated that Saddam hoped to restart his weapons programs primarily for defense against Iran.

At the same time, the report said that "the former regime had no formal written strategy or plan for the revival of WMD after the sanctions."

The report found that Iraq's "ability to reconstitute a nuclear weapons program progressively decayed" after 1991 -- and a nuclear weapon would have been years away.

Bush reiterated in October his position that Saddam had to go.

"He was a threat we had to confront, and America and the world are safer for our actions," he said. Democrats, however, didn't buy the president's position.

Bush's opponent in the presidential race, Sen. John Kerry, said the same day: "Mr. President, the American people deserve more than spin about this war.

"They deserve facts that represent reality, not carefully polished arguments and points that are simply calculated to align with a preconceived conception."

In Britain, Prime Minister Tony Blair faced similar criticism.

He told his party's annual conference in September that the "evidence about Saddam having actual biological and chemical weapons, as opposed to the capability to develop them, has turned out to be wrong."

"I can apologize for the information that turned out to be wrong," Blair said. "But I can't, sincerely at least, apologize for removing Saddam."